The invention relates to a method of and apparatus for protecting a ship from missiles with spectrally filtering infra-red target seeking heads.
In a battle situation, ships must be protected from an attack by rockets which are equipped with infra-red seeking heads. Seeking heads identify their target on a basis of an emission which distinguishes the ship from its surroundings. In recent times, seeking heads have been used which work on two frequencies, so-called two-colour seeking heads. These seeking heads evaluate the infra-red rays both in the short wave range, i.e. approx. 0.9 to 3 .mu.m, and also in the medium wave range, approx. 3 to 5 .mu.m. The ratio of short wave to medium wave infra-red radiation is a characteristic parameter by which a ship can be very satisfactorily distinguished from dummy targets and the rays reflected by the sun from the surface of the water. The reflection of the sun on the water substantially delivers rays which fall only in the short wave infra-red range, so that the proportion of short wave infra-red rays to medium wave infra-red rays is shifted strongly in the direction of short wave infra-red radiation. For the protection of ships, fired infra-red dummy targets likewise have fractions of their radiation which fall within the short wave infra-red range. In contrast, a ship generally emits no radiation in the short wave infra-red range but emits considerable levels of radiation in the medium wave infra-red range, so that there is here an intense shift in the direction of the proportion of medium wave infra-red rays. This shift can be evaluated by "intelligent" seeking heads.
It is known from DE-OS 36 08 578 to safeguard ships from an attack by infra-red controlled attack weapons in that there is disposed at a distance from the ship a heat source intended to exceed the infra-red signature of the ship and so divert the missile. This source of infra-red radiation is so disposed that on the one hand it can be recognised by the seeking head as belonging to the ship and on the other offers a centre of radiation to which the missile flies whereby in the event of any detonation it is not intended that any damage be caused on the ship itself.
It is known from "Wehrtechnik", 2/89, pages 48 to 54, to protect ships from missiles fitted with seeking heads in that zonal flares are ejected which irradiate heat and imitate the infra-red signature of the ship in order in this way to guide the seeking head to these flares.
DE-OS 32 17 336 describes a method of and an apparatus for camouflaging water-borne vehicles in which sea water is pumped up and expelled forming a curtain of water which falls outside the ship and which screens the areas to be camouflaged.
On the basis of the physical circumstances, it is not possible to produce dummy pyrotechnic targets which have a similar signature or spectral intensity of radiation as a ship. The object of the invention there was to provide a method and an apparatus by which ships can be protected from missiles with two-colour seeking heads.
This problem is resolved by a method of protecting a ship from missiles with two-colour infra-red target seeking heads which is characterised in that an interference transmitter disposed on the ship emits short wave infra-red rays at least intermittently, the intensity of the radiation from the interference transmitter being so adjusted that the ratio of short wave to medium wave infra-red radiation is so shifted that the ship cannot be reliably recognised as a target for the two-colour infra-red target seeking head.